Iter 14d: remove Term::If as a redundancy

Term::If was semantically a subset of Term::Match on Bool. Per
CLAUDE.md the language must contain no redundancies; two AST nodes
for the same operation produces an authoring decision with no
semantic content and a duplicate codegen path. Removed.

Migration shape (applied to sum, sort, max3 fixtures):
  (if c a b) -> (match c (case (lit-bool true) a) (case _ b))

No schema version bump (per user direction): no third-party consumes
ailang/v0, so version ceremony is pure overhead. Edited AST and
fixtures in place; pinned hashes in hash.rs updated.

Implementer deviation, called out and justified: a tightly-scoped
lower_bool_match helper (~95 LOC) was needed in codegen because
the existing match path rejects i1 scrutinees and Pattern::Lit.
Helper accepts only the canonical two-arm migration shape, errors
on anything else, emits the same br/phi IR Term::If used to. No
generalisation of the ADT-match codegen.

Diff: 13 files, +286/-221 (net +65 LOC). AST got smaller
(one variant gone), form-(A) got smaller (one production gone),
typecheck got smaller (one branch gone). Codegen got slightly
larger by the bool-match helper.

Hash deltas: sum.sum, sort.insert, max3.max, max3.max3 changed.
All other defs (e.g. sum.main, sort.IntList, sort.sort,
sort.print_list, max3.main) kept bit-identical hashes — confirms
canonical-JSON byte format intact.

Verification: 76/76 tests green; sum->55, max3->17, sort->[1,1,2,
3,3,4,5,5,5,6,9] (identical to pre-migration). cargo doc 0 warnings.

Tail-call survey by implementer (informs 14e): print_list
recursions are already in tail position (rhs of seq inside match
arm); map/sort/insert recursions are NOT (constructor-blocked
inside Cons applications). 14e annotation will benefit terminal
recursions; ctor-blocked ones need accumulator-form rewrites in
source, not a compiler-side transform.

Decision 7 added to DESIGN.md. JOURNAL entry has the language-
completion sequence (14d done, 14e tail-calls, 14f GC, 15a stdlib).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

examples/sum.ail.json

@@ -15,8 +15,8 @@
       "params": ["n"],
       "doc": "rekursive Summe 0..=n",
       "body": {
-        "t": "if",
-        "cond": {
+        "t": "match",
+        "scrutinee": {
           "t": "app",
           "fn": { "t": "var", "name": "==" },
           "args": [
@@ -24,28 +24,36 @@
             { "t": "lit", "lit": { "kind": "int", "value": 0 } }
           ]
         },
-        "then": { "t": "lit", "lit": { "kind": "int", "value": 0 } },
-        "else": {
-          "t": "app",
-          "fn": { "t": "var", "name": "+" },
-          "args": [
-            { "t": "var", "name": "n" },
-            {
+        "arms": [
+          {
+            "pat": { "p": "lit", "lit": { "kind": "bool", "value": true } },
+            "body": { "t": "lit", "lit": { "kind": "int", "value": 0 } }
+          },
+          {
+            "pat": { "p": "wild" },
+            "body": {
               "t": "app",
-              "fn": { "t": "var", "name": "sum" },
+              "fn": { "t": "var", "name": "+" },
               "args": [
+                { "t": "var", "name": "n" },
                 {
                   "t": "app",
-                  "fn": { "t": "var", "name": "-" },
+                  "fn": { "t": "var", "name": "sum" },
                   "args": [
-                    { "t": "var", "name": "n" },
-                    { "t": "lit", "lit": { "kind": "int", "value": 1 } }
+                    {
+                      "t": "app",
+                      "fn": { "t": "var", "name": "-" },
+                      "args": [
+                        { "t": "var", "name": "n" },
+                        { "t": "lit", "lit": { "kind": "int", "value": 1 } }
+                      ]
+                    }
                   ]
                 }
               ]
             }
-          ]
-        }
+          }
+        ]
       }
     },
     {